Our group is focused on classifying, identifying and studying the structure and functions of unknown egg proteins of invasive snails, agricultural plague and parasite vectors. We endeavour to understand the snail reproductive strategies from a biochemical perspective and, at the same time, to select some of these new proteins with potentials as bioactive compounds to exploit its application in Biomedicine.

Importance of the study of snail proteins

The knowledge of the structure and protein function is of key relevance for the understanding of all the biological processes. Gastropod molluscs are a source of bioactive molecules commonly used in Pharmacology and Medicine, since they have an outstanding diversity of compounds as reflection of their long evolutionary history. However, proteins of mollusc eggs are very little investigated. Our research group is studying them taking as a model those of Pomacea canaliculata (Lamarck, 1822), also called ampularia, an aquatic snail, worldwide invader which has turned out to be a plague for rice fields. Its uncontrolled expansion entailed the advance of a vector nematode parasite, responsible for human eosinophilic meningoencephalitis in Asia and Latin America. Its eggs strongly coloured by pigmented proteins almost have no predators.

Questions expected to answer

What kind of proteins do the eggs of this snail have?
Which are the properties of these proteins and what role do they play in the defence mechanism of the embryos?
Doe they have any application as tools in Biomedicine?

Employed methodology

Our group uses a multidisciplinary approach with collaborations of other research groups of our country and abroad in order to answer these questions, usually employing a combination of methodologies such as biochemical, molecular biology, biophysics, cellular biology, histopathological and bioassays with laboratory animals. Some of the techniques used are described as follows:

Determination of amino acid sequence.

Study of biochemical activity of inhibitors, lectins, enzymes isolated from the eggs.

Study of structure/function of proteins through dispersion of angle x-rays and biophysical techniques.

Microbiological studies of inhibition of bacterial growth.

In vitro studies of toxicity and interaction with cultured tumour cells.

Basic immunological studies.

Toxicity bioassays in murine model.

Use of optical and electronic microscopy for histopathological studies, effects on the nervous and digestive systems of potential predators

Main results

We studied the proteome of egg fluid and demonstrated that P. canaliculata has achieved a fascinating antipredatory defence mechanism where perivitellins play a central role, providing the embryos with one of the best defences in animals at biochemical level. We characterize major perivitellins (PcOvo y PcPV2) that participate in the defence as follows:

PcOvo caroprotein provides photoprotective and antioxidant compounds which at the same time give an intense colour. Its striking colouring would warn potential predators of the presence of various protein toxins of perivitellin fluid surrounding the embryo. PcOvo also has associated an activity as protease inhibitor of gastrointestinal tract of the predator, limiting the digestion of egg nutrients (antidigestive defence). Orally administered, it diminishes the growth rate in rats and impedes nutrient acquisition.

PcPV2 is lethal for rodents and is the first protein toxin described within an egg. Its structure differs from all other animal toxins since it combines a lectin subunit that recognizes specific sequences of membrane sugars, and a subunit that forms pores in the membrane. Despite the fact that there is no equal in animals, it is similar to some toxins type AB described in seeds and to the botulinum toxin. Whether this novel defence system is present in the eggs of other species remains unknown. We continue studying its properties and mechanism of action. However, we study the major egg protein ofPomacea scalaris so-called scalarin (PsSC) that provides the eggs with a striking rose-salmon colour that could function as a warning signal. We demonstrated that it is a powerful lectin that shows, nevertheless, many structural and functional similarities with PcOvo, that it is not.

We are studying its defence function as toxin lectin on the digestive system and its potential as biomarker of tumour cells. Other gastropod lectins have impact on medical practice and are commercialized to improve the pharmacokinetics of glycoprotein drugs or in the diagnosis of diseases such as tumour markers.

The structure and function of these three proteins are very resistant to high temperatures, to a very range of pH and to gastrointestinal digestion, what allows reaching biologically active intestines, highlighting even more its biotechnological application.

Evolutional and ecological implications

The selection pressure exerted by predators and hostile environment on the eggs would lead to the acquisition of new properties to endure the air development of an aquatic animal. At biochemical level it seems that these adaptations would involve a new type of perivitellins that besides being a reserve protein they are multifunctional compounds provided with very efficient defences against predation together with protective properties of the embryo facing hostile environment conditions.
The presence of eggs protected with proteins of these characteristics has not been found in other members of the animal kingdom, but it is similar to the plant defences against herbivory.